Monday, July 28, 2008

A cold front pushing across southern MB today will bring an increasing threat of thunderstorms today.. with the possibility of severe thunderstorms bringing large hail and possible tornadoes to portions of southern MB this afternoon into this evening. This same system produced numerous reports of severe weather across southern SK Sunday with at least 4 tornado reports. Residents of southern MB should stay tuned to updated forecasts and possible watches and warnings today on this potential severe weather outbreak.

Thursday, July 17, 2008

Forecasts for the weekend appear rather pessimistic for Winnipeg and southern Manitoba with showers forecast for both Saturday and Sunday and high temperatures only near 20C. But will it be that bad? Other computer models are more optimistic for the weekend showing more typical summerlike weather with only scattered showers and possible thunderstorms over the weekend, but dry most of the time, along with some sun and increasing humidity. The Canadian GLB seems to be the most aggressive with an impulse moving through the northern plains, generating a wide swath of heavy convective precipitation over southern MB. Who's right? We'll have to see what the trends are over the next run or two, but at this point, I'm thinking this weekend will not be a total washout as the GLB suggests, with partly sunny skies, more humid conditions giving scattered showers and thunderstorms at times, and high temperatures in the 22-25C range. Rest assured, this will not be a repeat of last Saturday's wet and wild weather!

Sunday, July 13, 2008

An intense storm system moved northeast of Berens River Saturday bringing a large swath of rain and strong winds over southern and central MB. The storm system.. which deepened to 984 mb.. was more typical of a fall-type storm system that commonly brings strong winds and rain to Manitoba. But such a system is unusual for the middle of July, and prompted the issuance of a rare July gale warning over the MB lakes where wind gusts over 45 kt were recorded on the eastern shores of Lake Winnipeg and Lake Manitoba. The strong winds extended over all areas of southern MB resulting in numerous broken tree branches across the area. Rainfall with this system ranged from 10-20 mm over Winnipeg and the southern Interlake to 50-75 mm over the northern lakes in places like Grand Rapids and Norway House.

Friday, July 11, 2008

On this date in 1936, Winnipeg registered its hottest day ever when the thermometer hit an unprecedented high of 42.2C(108F). In 136 years of weather records in the city (since 1872), Winnipeg has never recorded such an extreme temperature. The milestone was reached during a historic and unparalleled heat wave that gripped much of central and eastern North America that July. Many high temperature records in the US and Canada still stand from this historic heat wave. (see Chris Burt's entry on the 1936 heat wave)

Front page of the Winnipeg Evening Tribune, Monday July 13 1936after Winnipeg's hottest and deadliest weekend on record

In Winnipeg, the heat wave started on July 5th and persisted for 2 weeks before easing on the 18th. From July 5-17, Winnipeg recorded 13 consecutive days above 30C, the longest such streak in Winnipeg history. During that stretch, 10 daily record highs were set or equalled which remain unbroken to this day.. an unparalleled feat in Winnipeg climate history. 9 of those days were 35C or more with 2 days hitting over 40C, including Winnipeg's all time mark of 42.2C on the 11th. The average daily high temperature during this period was an incredible 36.4C. Nighttime offered little relief from the heat with overnight lows rarely dropping below the 20C mark. In particular, the night of July 11-12th must have been unbearable for Winnipeg residents. After hitting an all time high of 42.2C on the 11th, the thermometer dropped to a "low" of only 28.3C the following morning, Winnipeg's warmest ever nighttime low and the only time on record that the daily minimum temperature has remained above 25C in Winnipeg. In fact, on that night the temperature was at or above 30C most of the night. Imagine living in those conditions without air conditioning! The heat was so unbearable, many residents were forced to sleep outside to escape the heat of non-airconditioned buildings. For many residents, the heat was too much with at least 70 heat related deaths recorded in southern MB, including at least 31 in Winnipeg alone along with another 40 hospitalized for heat prostration (as reported by Winnipeg Tribune). That death toll makes the 1936 heat wave the deadliest weather related event in Winnipeg history.

Reconstruction of hourly temperatures in Winnipeg on July 11 1936Hourly temperatures are estimated based on 3 known values that day

Even hotter temperatures occurred elsewhere in Southern Manitoba during the 1936 heat wave. Emerson MB near the US border recorded 13 consecutive days over 35C between July 5th and 17th, with an average high of an incredible 39.9C over the 13 day period. The heat wave included a phenomenal 7 days of 40C or more including a maximum of 44.4C on the 12th, Manitoba's hottest temperature on record. In fact, it was Canada's hottest ever temperature until Midale and Yellow Grass in southeast Saskatchewan hit 45.0C the following summer. During July 1936, Emerson registered 27 days of 30C or more, with an average high of 34.6C for the month, almost Arizona like. Between the 5th and the 13th, the town registered a remarkable 9 consecutive days of 100F or higher (37.8C)

Daily temperatures at Winnipeg and Emersonduring the July 1936 heat wave

Further south in North Dakota, the town of Steele (between Bismarck and Jamestown) hit an unfathomable 49.4C (121F) on July 6th 1936 - the hottest temperature in North Dakota history. Such a temperature rivals the type of extreme heat found in the US desert southwest, and is almost as hot as Phoenix AZ's all time high of 50C/122F! The weather observer in Steele (Mrs R.G. Armstrong) noted on her weather summary that "flowers on trees and shrubbery were cooked" due to the intense heat that day. July 6th 1936 saw all time highs established in Bismarck (45.6C/114F), Fargo (45.6C/114F) and Jamestown (47.8C/118F), records that still stand to this day. (read more about North Dakota heat here)

High temperatures (F) - North Dakota - July 6 1936
The hottest day in North Dakota history set all time highs
in Bismarck and Fargo (114F), as well as the state (Steele, 121F)

By all accounts, the 1936 heat wave was an historic and unparalleled heat wave that has yet to be matched in weather record keeping. 6 years of drought had left the Prairies bone dry and crops withered, allowing maximum heating of the surface during the hot summer months. In the July 1936 event, a huge upper ridge must have developed over central North America, allowing extreme temperatures to reach well north into southern Canada. The upper pattern would have been stationary for at least 2 weeks, allowing the unrelenting heat to persist for days on end, intensified by the early July sun. Whatever the cause, the conditions that led to the 1936 heat wave have never come together again to the extent they did 72 years ago this week. So as you complain about this year's cool summer weather, try to think what residents of Manitoba had to endure during the granddaddy of all heat waves - July 1936.

It was so hot during the 1936 heat wave, may residents were forcedto sleep outside. This scene was from St Paul Minnesota

Southern MB remains under a severe thunderstorm watch this afternoon as a low pressure system over eastern North Dakota draws a warm and humid airmass northward. Morning thunderstorm activity has pushed into the northern Interlake this afternoon, while the south gets a temporary reprieve from the severe weather. However, as the North Dakota low moves into southern MB later today, a flow of warm and humid air will be drawn over southeast MB while a cold front pushes in from the west. This will set the stage for additional severe thunderstorms to develop, especially over the Red River valley and southeast MB. Strong winds and large hail will be the main threat, however favourable wind shear profiles over southeast MB may give the threat of tornadoes with any supercell thunderstorms that develop.

As this low pressure system moves north into the Interlake tonight, it will deepen into an almost fall-like storm by Saturday morning with strong west to northwest winds developing on the backside of the low. Gale warnings have been issued for the MB lakes with west to northwest gales of 40 knots forecast for Saturday. This will likely generate large waves over the south basins of Lakes Winnipeg and Manitoba with possible shoreline erosion problems on eastern and southern shores. Temperatures will also be unseasonably cool Saturday with highs only in the mid teens along with occasional rain making it feel more like September than mid July. Not a good day for Grand Beach unless you like windsurfing!

Wednesday, July 09, 2008

Looks like another setup for possible severe thunderstorms to develop across Southern MB late Thursday into Thursday evening. A low pressure system and trough will be moving across southern SK Thursday moving to the SK/MB border by Thursday evening. A warm front extending east of this system will lie across the MB/ND border by evening which will be the focus for thunderstorm development. South of the warm front, warm and humid air will be advecting north from the Dakotas and will nose into Southern MB especially south and west of Winnipeg. Favourable low level wind shear and an increasing jet stream aloft will set the stage for supercell storms to develop across the Dakotas and southwest MB, with the potential for large hail and possible tornadoes. The limiting factor in this setup will be how much moisture can de drawn into this system in a short period of time, since dewpoints are quite low across the northern Plains today. As a result, the severe weather threat may be late Thursday before sufficient moisture can be drawn into this system. Stay tuned..

Thursday, July 03, 2008

Hot weather will be returning to southern MB over the next couple of days with highs approaching 30 degrees Friday, likely reaching the low 30s on Saturday. Saturday will also see increasing humidity levels as southerly winds tap more humid air to our south and advect it north. This will set the stage for possible strong to severe thunderstorms to develop by Saturday evening over the Red River valley as a weak cold front approaches from the west. Behind the cold front, more comfortable conditions will return for Sunday with seasonably warm and less humid conditions.

Tuesday, July 01, 2008

Mother Nature has served up some of her own Canada Day fireworks today with some severe thunderstorms firing up over southeast MB ahead of a cold front pushing through from the north. The front moved through Winnipeg just before 5 pm, shifting winds into the north and dropping temperatures and humidity levels noticeably bringing relief from the hot and humid conditions this afternoon. The brisk northerly winds however are ushering in a large area of smoke aloft from northern SK forest fires into southern MB. Residents of southern MB will notice a hazy look to the sky this evening along with locally reduced visibilities, a brilliant red sunset, and a distinct smell of smoke.